A chordate is an animal constituting the phylum Chordata. During some period of their life cycle, chordates possess a notochord, a dorsal nerve cord, pharyngeal slits, an endostyle, a post-anal tail: these five anatomical features define this phylum. Chordates are bilaterally symmetric; the Chordata and Ambulacraria together form the superphylum Deuterostomia. Chordates are divided into three subphyla: Vertebrata. There are extinct taxa such as the Vetulicolia. Hemichordata has been presented as a fourth chordate subphylum, but now is treated as a separate phylum: hemichordates and Echinodermata form the Ambulacraria, the sister phylum of the Chordates. Of the more than 65,000 living species of chordates, about half are bony fish that are members of the superclass Osteichthyes. Chordate fossils have been found from as early as the Cambrian explosion, 541 million years ago. Cladistically, vertebrates - chordates with the notochord replaced by a vertebral column during development - are considered to be a subgroup of the clade Craniata, which consists of chordates with a skull.
The Craniata and Tunicata compose the clade Olfactores. Chordates form a phylum of animals that are defined by having at some stage in their lives all of the following anatomical features: A notochord, a stiff rod of cartilage that extends along the inside of the body. Among the vertebrate sub-group of chordates the notochord develops into the spine, in wholly aquatic species this helps the animal to swim by flexing its tail. A dorsal neural tube. In fish and other vertebrates, this develops into the spinal cord, the main communications trunk of the nervous system. Pharyngeal slits; the pharynx is the part of the throat behind the mouth. In fish, the slits are modified to form gills, but in some other chordates they are part of a filter-feeding system that extracts particles of food from the water in which the animals live. Post-anal tail. A muscular tail that extends backwards behind the anus. An endostyle; this is a groove in the ventral wall of the pharynx. In filter-feeding species it produces mucus to gather food particles, which helps in transporting food to the esophagus.
It stores iodine, may be a precursor of the vertebrate thyroid gland. There are soft constraints that separate chordates from certain other biological lineages, but are not part of the formal definition: All chordates are deuterostomes; this means. All chordates are based on a bilateral body plan. All chordates are coelomates, have a fluid filled body cavity called a coelom with a complete lining called peritoneum derived from mesoderm; the following schema is from the third edition of Vertebrate Palaeontology. The invertebrate chordate classes are from Fishes of the World. While it is structured so as to reflect evolutionary relationships, it retains the traditional ranks used in Linnaean taxonomy. Phylum Chordata †Vetulicolia? Subphylum Cephalochordata – Class Leptocardii Clade Olfactores Subphylum Tunicata – Class Ascidiacea Class Thaliacea Class Appendicularia Class Sorberacea Subphylum Vertebrata Infraphylum incertae sedis Cyclostomata Superclass'Agnatha' paraphyletic Class Myxini Class Petromyzontida or Hyperoartia Class †Conodonta Class †Myllokunmingiida Class †Pteraspidomorphi Class †Thelodonti Class †Anaspida Class †Cephalaspidomorphi Infraphylum Gnathostomata Class †Placodermi Class Chondrichthyes Class †Acanthodii Superclass Osteichthyes Class Actinopterygii Class Sarcopterygii Superclass Tetrapoda Class Amphibia Class Sauropsida Class Synapsida Craniates, one of the three subdivisions of chordates, all have distinct skulls.
They include the hagfish. Michael J. Benton commented that "craniates are characterized by their heads, just as chordates, or all deuterostomes, are by their tails". Most craniates are vertebrates; these consist of a series of bony or cartilaginous cylindrical vertebrae with neural arches that protect the spinal cord, with projections that link the vertebrae. However hagfish have incomplete braincases and no vertebrae, are therefore not regarded as vertebrates, but as members of the craniates, the group from which vertebrates are thought to have evolved; however the cladistic exclusion of hagfish from the vertebrates is controversial, as they ma
The crimson-rumped toucanet is a species of bird in the Ramphastidae family. It is found in humid Andean forests in Ecuador and Venezuela, its plumage is overall green, except for tail-tip. The bill is maroon with a white band at the base, it weighs from 141 -- 232 grams. The crimson-rumped toucanet was described in the genus Pteroglossus. Alternate names include chestnut-billed emerald-toucanet, crimson-rumped aracari and red-rumped green-toucanet Two subspecies are recognized: A. h. haematopygus -: Found in Colombia and western Venezuela A. h. sexnotatus - Gould, 1868: Originally described as a separate species. Found in south-western Colombia and western Ecuador
Toucans are members of the Neotropical near passerine bird family Ramphastidae. The Ramphastidae are most related to the American barbets, they have large, often-colorful bills. The family includes five genera and over forty different species. Toucans are arboreal and lay 2–21 white eggs in their nests, they make their nests in tree hollows and holes excavated by other animals such as woodpeckers—the toucan bill has limited use as an excavation tool. When the eggs hatch, the young emerge naked, without any down. Toucans do not migrate. Toucans are found in pairs or small flocks, they sometimes fence with their bills and wrestle, which scientists hypothesize they do to establish dominance hierarchies. The name of this bird group is derived from the Tupi word tukana, via Portuguese; the family includes toucans and toucanets. The toucan family has five extant genera as follows: Toucans range in size from the lettered aracari, at 130 g and 29 cm, to the toco toucan, at 680 g and 63 cm, their bodies are compact.
The tail varies in length, from half the length to the whole length of the body. The neck is thick; the wings are small, as they are forest-dwelling birds who only need to travel short distances, are of about the same span as the bill-tip-to-tail-tip measurements of the bird. The legs of the toucan are rather short, their toes are arranged in pairs with the fourth toes turned backward. The majority of toucans do not show any sexual dimorphism in their coloration, the genus Selenidera being the most notable exception to this rule. However, the bills of female toucans are shorter and sometimes straighter, giving more of a "blocky" impression compared to male bills; the feathers in the genus containing the largest toucans are purple, with touches of white and scarlet, black. The underparts of the araçaris are yellow, crossed by one or more red bands; the toucanets, have green plumage with blue markings. The colorful and large bill, which in some large species measures more than half the length of the body, is the hallmark of toucans.
Despite its size, the toucan's bill is light, being composed of bone struts filled with spongy tissue of keratin between them. This deep light-weight construction is the most efficient in terms of strength/weight ratio - like a bridge truss as compared to a beam - so would explain the depth of the bill in the absence of any adaptive penalties associated with a deeper bill as compared with a more compact bill of equal length, which would have to be heavier; the bill has forward-facing serrations resembling teeth, which led naturalists to believe that toucans captured fish and were carnivorous. Researchers have discovered that the large bill of the toucan is a efficient thermoregulation system, though its size may still be advantageous in other ways, it does aid in their feeding behavior, it has been theorized that the bill may intimidate smaller birds, so that the toucan may plunder nests undisturbed. The beak allows the bird to reach deep into tree-holes to access food unavailable to other birds, to ransack suspended nests built by smaller birds.
A toucan's tongue is long, narrow and singularly frayed on each side, adding to its sensitivity as a tasting organ. A structural complex unique to toucans involves the modification of several tail vertebrae; the rear three vertebrae are attached to the spine by a ball and socket joint. Because of this, toucans may snap their tail forward; this is the posture in which they sleep appearing as a ball of feathers, with the tip of the tail sticking out over the head. Toucans are native to the Neotropics, from Southern Mexico, through Central America, into South America south to northern Argentina, they live in the lowland tropics, but the montane species from the genus Andigena reach temperate climates at high altitudes in the Andes and can be found up to the tree line. For the most part the toucans are forest species, restricted to primary forests, they will enter secondary forests to forage, but are limited to forests with large old trees that have holes large enough to breed in. Toucans are poor dispersers across water, have not reached the West Indies.
The only non-forest living toucan is the toco toucan, found in savannah with forest patches and open woodlands. Toucans are social and most species occur in groups of up to 20 or more birds for most of the time. Pairs may retire from the groups during the breeding season return with their offspring after the breeding season. Larger groups may form during irruptions, migration or around a large fruiting tree. Toucans spend time sparring with their bills, tag-chasing and calling, during the long time it takes for fruit to digest; these behaviours may be related to maintenance of the pair bond or establishing dominance hierarchies, but the digestion time of fruit, which can take up to 75 minutes during which the toucan can't feed, provide this social time. Toucans are frugivorous, but are opportunistically omnivorous and will take prey such as insects, smaller birds
The pale-mandibled aracari, or pale-mandibled araçari, is a species of bird in the Ramphastidae family. It is found in western Peru; the pale-mandibled aracari is considered to be a subspecies of the collared aracari by some authorities. Alternate names for the pale-mandibled aracari include the pale-billed araçari, red-backed aracari, red-rumped aracari and scarlet-rumped aracari
The blue-banded toucanet is a species of bird in the family Ramphastidae. It is found in Peru, its natural habitat is subtropical or tropical moist montane forests. It is 38 -- 43 cm long; the alternate name blue-throated toucanet should not be confused with the species of the same name, Aulacorhynchus caeruleogularis